378 Carbohjid rates of the Leaf of the Potato 



As in the case of the maiifjold leaves, the polarisation results for 

 saccharose are generally considerably higher — often "20 to 30 per cent, 

 higher — than the reduction values*. The two methods only give 



approximately the same results when j approximates to 1 (e.g. at 



8 a.m. and 12 noon, when A (invertase) is only 2-7 and G-lt per cent.). 



When the dextrose appears to disappear (t = Oj the divergences (A) 



are greatest (e.g. G a.m., 10 a.m., 2 p.m., 4 p.m., 10 p.m.). As showing 



the presence of two tiistinct and oppositely active impurities, it is 



interesting that between 6 a.m. and 1 p.m. when the laevulose on the 



whole appears to increase (see Fig. 3) a rise in the apparent dextrose 



corresponds with a diminution in the difference between polarisation 



and reduction values for saccharose, and vice versa; but from -1 p.m. 



to 10 p.m. (laevulose falling) an increase in the apparent dextrose carries 



with it an increase in the divergence, whilst a fall in the dextrose is 



accompanied by an opposite result (compare the figures in Table VI 



with the curves in Fig. 3). Between 10 p.m. and 2 a.m., when the 



laevulose again appears to rise and fall, the difference between the two 



sets of values becomes less and less (invertase figures) and finally negative. 



It is interesting to compare the following figures; 



Sunrise 



10 p.m. Midnight 2 a in. 4 a.m. 6 a.m 



Rotation not ac- 

 counted for by 

 thehexoses ... -0-062'' -0-010" -0-002° +0-015° -0-081° 



A (invertase) be- 

 tween sacchar- 

 ose values ... -fll-0% + 3-8% -12-5% +74% •fl7-2% 



The abrupt change between 2 a.m. and 4 a.m. (corresponding with 

 the sudden fall to zero of the apparent laevulose) from a negative 

 rotation not accounted for to a high positive value, and a negative 

 difference — 12-5 per cent, to a high positive value + 74 per cent., is 

 followed, immediately after sunrise, by equally great changes in the 



' If tlic discrepancy between the results for saccharo.se were due solely to an amino- 

 acid or amide such as asparaginc, one would expect the divergence to be diminished by 

 taking the first (direct) polarisation after saturating the solution with suliihur tlio.xide 

 so as to make it strongly acid (see I'ellet, Dn.satje du Sucre jxir Inversion, 1913). As a 

 matter of fact in the case of the potato whether the direct reading was taken (as has been 

 usual in our experiments) in practically neutral solution or whether it was taken in acid 

 solution (SO,) made very little difference in the majority of cases, the figures usually 

 being very high as compared with the reduction values. 



